Divorce JSON and KCL (#4436)

Removes JSON from the KCL object model. Closes https://github.com/KittyCAD/modeling-app/issues/1130 -- it was filed on Nov 27 last year. Hopefully I close it before its one year anniversary.

Changes:

- Removed the UserVal variant from `enum KclValue`. That variant held JSON data.
- Replaced it with several new variants like Number, String, Array (of KCL values), Object (where keys are String and values are KCL values)
- Added a dedicated Sketch variant to KclValue. We used to have a variant like this, but I removed it as an experimental approach to fix this issue. Eventually I decided to undo it and use the approach of this PR instead.
- Removed the `impl_from_arg_via_json` macro, which implemented conversion from KclValue to Rust types by matching the KclValue to its UserVal variant, grabbing the JSON, then deserializing that into the desired Rust type. 
- Instead, replaced it with manual conversion from KclValue to Rust types, using some convenience macros like `field!`

src/wasm-lib/tests/executor/main.rs

@@ -1354,7 +1354,7 @@ secondSketch = startSketchOn(part001, '')
     assert!(result.is_err());
     assert_eq!(
         result.err().unwrap().to_string(),
-        r#"semantic: KclErrorDetails { source_ranges: [SourceRange([260, 286, 0])], message: "Argument at index 1 was supposed to be type kcl_lib::std::sketch::FaceTag but found string (text)" }"#
+        r#"semantic: KclErrorDetails { source_ranges: [SourceRange([260, 286, 0])], message: "Argument at index 1 was supposed to be type Option<kcl_lib::std::sketch::FaceTag> but found string (text)" }"#
     );
 }